In order to support a vibration generating section such as an engine on a vibration receiving section such as a vehicle body, and to attenuate and absorb vibration transmitted from the vibration generating section towards the vibration receiving section, known vibration isolation structures support the vibration generating section on the vibration receiving section by employing a composite laminated member formed from alternately stacked plural hard plates with rigid characteristics, for example steel plates, and plural soft plates with viscoelastic characteristics, made from for example rubber. Such vibration isolation structures attenuate and absorb vibration generated by the vibration generating section using the composite laminated member, and prevent amplification of vibration due to resonance by interposing the composite laminated member between the vibration generating section and the vibration receiving section. The level of vibration transmitted to the vibration receiving section is thereby reduced.
Such composite laminated bodies are made so as to be capable of comparatively large deformation in the horizontal direction in a state supporting the weight of the vibration generating section. The composite laminated member accordingly mainly undergoes shear deformation in the horizontal direction when vibration is received in a state in which the composite laminated member is supporting load from the vibration generating section, namely in a state in which positive pressure is placed on the composite laminated member. However, since the bottom end side of the vibration isolation structure is restricted by the vibration receiving section side, twisting deformation occurs in the composite laminated member when a vibration with large amplitude is input. Accompanying the occurrence of twisting deformation, a compression load acts on an amplitude direction first end portion of the composite laminated member, and tensional load acts on an amplitude direction second end portion. The compression load and the tensional load acting on the composite laminated member increase as the twisting deformation of the composite laminated member increases, namely as the amplitude of the input vibration increases. The free surface area of the composite laminated member is small compared to the comparatively large constrained face, therefore a concentration of hydrostatic stress occurs at a central portion of the constrained face when tensional load is acting, and damage can be easily sustained.
In the technology disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2008-75743, a reduction to internal stress of a soft member is achieved by increasing the thickness of the soft member at portions where twisting deformation causes hydrostatic stress to become high, and by increasing the free surface area of the soft member. However, sufficient reduction to hydrostatic stress cannot be achieved merely by this increase in thickness, and further improvements are demanded in order to effectively suppress damage to the composite laminated member.